1. Field of the Invention
The present invention relates to a slide rail device for a seat including an automotive seat which is operable to adjust the position of the seat in the fore-and-aft direction, and is particularly directed to a slide rail device of the type mounted laterally of a seat frame together with a seat belt anchor member.
2. Description of Prior Art
In most instances, an automotive seat is supported via a slide rail device upon the floor of an automobile permitting its position to be adjusted in the fore-and-aft direction. In particular, among various slide rail devices, a vertical type of slide rail device is known wherein upper and lower rail members are slidably fitted together in an upright or vertical fashion to permit them to be easily mounted to one lateral wall of a seat cushion frame.
Reference is made to FIG. 1 which shows a typical conventional vertical type of seat rail device (110) mounted laterally of a seat cushion frame (116) which forms a part of a seat (not shown). According thereto, an upper rail member (118) has an upper engagement part (128) and a lower engagement part (129), whereas a lower rail member (114) has an upwardly projected engagement part (124) and a downwardly projected engagement part (125). As shown, the upper and lower engagement parts (124)(125) of the lower rail member (114) are respectively slidably engaged in the upwardly and downwardly projected engagement parts (124)(125) via upper and lower sliders (120)(121).
The lower rail member (114) is fixed at its lower end side to the floor (F) of an automobile. The upper rail member (118) is fixed at its vertical lateral side to the lateral wall of seat cushion frame (116), with a seat belt anchor (132) sandwiched therebetween. The seat belt anchor (132) has a belt socket (BS) into which a knuckle of seat belt is to be engaged.
In such an emergency case as a sudden deceleration or collision, a great load (i.e. pulling force) is applied from an occupant sitting on the seat, via the seat belt, to both of the slide rail device (110) and seat belt anchor (132). In this case, the load is dispersed there, exerting an approx. 45-degree upwardly slant forward force (not shown) and apporx. 15-degree inwardly slant force (Z) upon the seat belt anchor (132), and further such inwardly slant component force (Z) applies a vertically upward and horizontally inward component forces (X)(Y) to the slide rail device (110).
Against this emergency case, the present conventional slide rail (110) is provided with a lock section (114a) at the lower end thereof. Namely, the lock section (114a) is formed by a pair of vertically opposed lock lugs (136) (138), each extending continuously from the lower engagement part (129) of the upper rail member (128), and an upturned lock lug (138) extending continuously from the lower end of the lower rail member (114). With this structure, in a collision case or the like, the above-discussed component forces (X)(Y)(Z) are produced to forcibly engage the two lock lugs (136)(138) with the lower engagement part (125) and upturned lock lug (138), respectively, thereby locking both upper and lower rail members (128)(114) against their separation.
However, such conventional construction of slide rail device (110) has been found defective in that, as understandable from FIG. 1, a spot where a stress is created most intensively from the two component forces (X)(Y) is the base area of the lower engagement part (125) which is threfore prone to deformation, thus inevitably requiring a special design to give a sufficient strength to that lower engagement part (125). Further, the upturned lock lug (138) produces a most intensive stress from the horizontally inward component force (Y), which is also prone to deformation, requiring a sufficient strength thereto.
One can contemplate on adding a separate reinforcing member to those week spots, and in fact, the same reinforcing process has been done in most of known slide rail devices. But, this results in increasing the number of parts and making complicated the seat assembling steps, which is undesirable because it is very troublesome to workers.